Liquid crystal display device having array substrate of color filter on thin film transistor structure and manufacturing method thereof

ABSTRACT

A liquid crystal display device having an array substrate of a color filter on a thin film transistor structure and a manufacturing method thereof are disclosed in the present invention. The liquid crystal display device having an array substrate includes an array substrate, a plurality of gate lines and data lines over the substrate, the gate and data lines defining a pixel region, a thin film transistor formed at each crossing region of the gate lines and the data lines, the thin film transistor including a gate electrode, an active layer, a source electrode, and a drain electrode, a black matrix over the thin film transistor, exposing a portion of the drain electrode, a first pixel electrode at the pixel region, contacting the exposed portion of the drain electrode, a color filter on the first pixel electrode at the pixel region, and a second pixel electrode on the color filter, directly contacting the first pixel electrode.

[0001] This application claims the benefit of the Korean Application No.P2002-036998 filed on Jun. 28, 2002, which is hereby incorporated byreference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a liquid crystal display device,and more particularly, to a liquid crystal display device having anarray substrate of a color filter on thin film transistor structure anda manufacturing method thereof. Although the present invention issuitable for a wide scope of applications, it is particularly suitablefor increasing an aperture ratio and simplifying the fabricationprocess.

[0004] 2. Discussion of the Related Art

[0005] In general, since flat panel display devices are thin, lightweight, and have low power consumption, they have been used for displaysof portable devices. Among the various types of flat panel displaydevices, liquid crystal display (LCD) devices are widely used for laptopcomputers and desktop computer monitors because of their superiority inresolution, color image display, and display quality.

[0006] Optical anisotropy and polarization properties of liquid crystalmolecules are utilized to generate a predetermined image. Liquid crystalmolecules have a specific alignment that results from their own peculiarcharacteristics. The specific alignment can be modified by electricfields that are applied upon the liquid crystal molecules. In otherwords, the electric fields applied upon the liquid crystal molecules canchange the alignment of the liquid crystal molecules. Due to opticalanisotropy, incident light is refracted according to the alignment ofthe liquid crystal molecules.

[0007] Specifically, the LCD devices include upper and lower substrateshaving electrodes that are spaced apart and face into each other, and aliquid crystal material is interposed therebetween. Accordingly, when avoltage is applied to the liquid crystal material through the electrodesof each substrate, an alignment direction of the liquid crystalmolecules is changed in accordance with the applied voltage in order todisplay images. By controlling the applied voltage, the LCD deviceprovides various transmittances for rays of light to display image data.

[0008] The liquid crystal display (LCD) devices are widely applied inoffice automation (OA) and video equipment due to their characteristicsof light weight, thin design, and low power consumption. Among differenttypes of LCD devices, active matrix LCDs (AM-LCDs) having thin filmtransistors and pixel electrodes arranged in a matrix form offer highresolution and superiority in displaying moving images. A typical LCDpanel has an upper substrate, a lower substrate, and a liquid crystalmaterial layer interposed therebetween. The upper substrate, referred toas a color filter substrate, includes a common electrode and colorfilters. The lower substrate, referred to as an array substrate,includes switching elements such as thin film transistors (TFT's) andpixel electrodes.

[0009] As previously described, the operation of an LCD device is basedon the principle that the alignment direction of the liquid crystalmolecules depends upon applied electric fields between the commonelectrode and the pixel electrode. Accordingly, the liquid crystalmolecules function as an optical modulation element having variableoptical characteristics that depend upon the polarity of the appliedvoltage.

[0010]FIG. 1 is an expanded perspective view illustrating a related artactive matrix LCD device. As shown in FIG. 1, the LCD device 11 includesan upper substrate 5, referred to as a color filter substrate, and alower substrate 22, referred to as an array substrate, having a liquidcrystal material layer 14 interposed therebetween. On the uppersubstrate 5, a black matrix 6, and a color filter layer 8 are formed ina shape of an array matrix including a plurality of red (R), green (G),and blue (B) color filters surrounded by corresponding portions of theblack matrix 6. Additionally, a common electrode 18 is formed on theupper substrate 5 to cover the color filter layer 8 and the black matrix6.

[0011] On the lower substrate 22, a plurality of thin film transistors Tare formed in a shape of an array matrix corresponding to the colorfilter layer 8. A plurality of crossing gate lines 13 and data lines 15are perpendicularly positioned such that each TFT T is located adjacentto each intersection of the gate lines 13 and the data lines 15.Furthermore, a plurality of pixel electrodes 17 are formed on a pixelregion P defined by the gate lines 13 and the data lines 15 of the lowersubstrate 22. The pixel electrode 17 includes a transparent conductivematerial having high transmissivity, such as indium-tin-oxide (ITO) orindium-zinc-oxide (IZO).

[0012] Still in FIG. 1, a storage capacitor C is disposed to correspondto each pixel P and connected in parallel to each pixel electrode 17.The storage capacitor C is comprised of a portion of the gate line 13 asa first capacitor electrode, an storage metal layer 30 as a secondcapacitor electrode, and an interposed insulator (reference numeral 16of FIG. 2). Since the storage metal layer 30 is connected to the pixelelectrode 17 through a contact hole, the storage capacitor Celectrically contacts the pixel electrode 17.

[0013] In the related art LCD device shown in FIG. 1, a scanning signalis applied to a gate electrode of the thin film transistor T through thegate line 13, and a data signal is applied to a source electrode of thethin film transistor T through the data line 15. As a result, the liquidcrystal molecules of the liquid crystal material layer 14 are alignedand arranged by operation of the thin film transistor T, and incidentlight passing through the liquid crystal layer 14 is controlled todisplay an image. However, since the pixel and common electrodes 17 and18 are positioned on the upper and lower substrates 5 and 22,respectively, the electric fields induced between the upper and lowersubstrates 5 and 22 are perpendicular to the surfaces of the upper andlower substrates 5 and 22.

[0014] When fabricating the LCD device 11 of FIG. 1, the upper substrate5 is aligned with and attached to the lower substrate 22. In thisprocess, the upper substrate 5 may be misaligned with the lowersubstrate 22 and light leakage may occur in the completed LCD device 11due to an error margin in attaching the upper and lower substrate 5 and22.

[0015]FIG. 2 is a schematic cross-sectional view taken along line II-IIof FIG. 1, illustrating a pixel of the related art liquid crystaldisplay (LCD) device.

[0016] As shown in FIG. 2, the related art LCD device includes the uppersubstrate 5, the lower substrate 22, and the liquid crystal layer 14.The upper and lower substrates 5 and 22 are spaced apart from eachother, and the liquid crystal layer 14 is interposed therebetween. Theupper and lower substrates 5 and 22 are often referred to as an arraysubstrate and a color filter substrate, respectively, because the colorfilter layer 8 is formed upon the upper substrate and a plurality ofarray elements are formed on the lower substrate 22.

[0017] In FIG. 2, the thin film transistor T is formed on the frontsurface of the lower substrate 22. The thin film transistor T includes agate electrode 32, an active layer 34, a source electrode 36, and adrain electrode 34. Between the gate electrode 32 and the active layer34, a gate insulation layer 16 is interposed to protect the gateelectrode 32. As shown in FIG. 1, the gate electrode 32 extends from thegate line 13 and the data electrode 36 extends from the data line 15.All of the gate, source, and drain electrodes 32, 36, and 38 are formedof a metallic material while the active layer 34 is formed of silicon. Apassivation layer 40 is formed on the thin film transistor T forprotection. In the pixel region P, the pixel electrode 17 that is formedof a transparent conductive material is disposed while contacting thedrain electrode 38 and the storage metal layer 30.

[0018] Meanwhile, as mentioned above, the gate electrode 13 acts as afirst electrode of the storage capacitor C and the storage metal layer30 acts as a second electrode of the storage capacitor C. Thus, the gateelectrode 13 and the storage metal layer 30 constitutes the storagecapacitor C with the interposed gate insulation layer 16.

[0019] Still referring to FIG. 2, the upper substrate 5 is spaced apartfrom the first substrate 22 over the thin film transistor T. On the rearsurface of the upper substrate 5, a black matrix 6 is disposed in theposition corresponding to the thin film transistor T and the gate line13. The black matrix 6 is formed on the entire surface of the uppersubstrate 5 and have openings corresponding to the pixel electrode 17 ofthe lower substrate 11, as shown in FIG. 1. The black matrix 22 preventslight leakage in the LCD panel except for the portion for the pixelelectrode 17. The black matrix 6 protects the thin film transistor Tfrom the light such that the black matrix 6 prevents generating of photocurrent in the thin film transistor T. The color filter layer 8 isformed on the rear surface of the upper substrate 5 to cover the blackmatrix 6. Each of the color filters 8 has one of the red, green, andblue colors and corresponds to one pixel region where the pixelelectrode 17 is located. A common electrode 18 formed of a transparentconductive material is disposed on the color filter layer 8 over theupper substrate 5.

[0020] In the related art LCD panel mentioned above, the pixel electrode17 has a one-to-one correspondence with one of the color filters.Furthermore, in order to prevent a crosstalk between the pixel electrode17 and the gate and data lines 13 and 15, the pixel electrode 17 isspaced apart from the data line 15 by the distance A and from the gateline 13 by the distance B, as shown in FIG. 2. The open spaces A and Bbetween the pixel electrode 17 and the data and gate line 15 and 13cause a malfunction such as light leakage in the LCD device. Namely, thelight leakage mainly occurs in the open spaces A and B so that the blackmatrix 6 formed on the upper substrate 5 should cover those open spacesA and B. However, when arranging the upper substrate 5 with the lowersubstrate 22 or vice versa, a misalignment may occur between the uppersubstrate 5 and the lower substrate 22. Therefore, the black matrix 6 isextended to cover those open spaces A and B. That is, the black matrix 6is designed to provide an aligning margin to prevent light leakage.However, in the case of extending the black matrix, an aperture ratio ofthe liquid crystal panel is reduced as much as the aligning margin ofthe black matrix 6. Moreover, if there are errors in the aligning marginof the black matrix 6, the light leakage occurs in the open spaces A andB, and deteriorates the image quality of the LCD device.

SUMMARY OF THE INVENTION

[0021] Accordingly, the present invention is directed to a liquidcrystal display device having an array substrate of a color filter on athin film transistor structure and a manufacturing method thereof thatsubstantially obviates one or more of problems due to limitations anddisadvantages of the related art.

[0022] Another object of the present invention is to provide an arraysubstrate for a liquid crystal display device, which provides a highaperture ratio.

[0023] Another object of the present invention is to provide a method offorming an array substrate for a liquid crystal display device, whichsimplifies a manufacturing process and increases a manufacturing yield.

[0024] Additional features and advantages of the invention will be setforth in the description which follows and in part will be apparent fromthe description, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

[0025] To achieve these and other advantages and in accordance with thepurpose of the present invention, as embodied and broadly described, aliquid crystal display device having an array substrate includes aplurality of gate lines and data lines over the array substrate, thegate and data lines defining a pixel region, a thin film transistorformed at each crossing region of the gate lines and the data lines, thethin film transistor including a gate electrode, an active layer, asource electrode, and a drain electrode, a black matrix over the thinfilm transistor, exposing a portion of the drain electrode, a firstpixel electrode at the pixel region, contacting the exposed portion ofthe drain electrode, a color filter on the first pixel electrode at thepixel region, and a second pixel electrode on the color filter,contacting the first pixel electrode.

[0026] The liquid crystal display device having an array substratefurther includes a first insulating layer between the gate electrode andthe active layer, and a second insulating layer between the black matrixand the thin film transistor. The first and second insulating layers areformed of an inorganic material selected from the group consisting ofsilicon nitride and silicon oxide.

[0027] The liquid crystal display device of the present inventionfurther includes a storage capacitor at the pixel region, whichcomprises an storage metal layer on the first insulating layer and aportion of the gate line acting as a first storage electrode. The secondpixel electrode contacts the storage metal layer through a storagecontact hole in the black matrix and the second insulating layer. Thefirst pixel electrode contacts the drain electrode through a draincontact hole in the black matrix and the second insulating layer.

[0028] Alternately, the black matrix exposes an end side portion of thedrain electrode, so that the first pixel electrode contacts the sideportion of the drain electrode. The liquid crystal display devicefurther includes an ohmic contact layer between the active layer and thesource and drain electrodes. Herein, the color filter is formed betweenthe first pixel electrode and the second pixel electrode.

[0029] In another aspect of the present invention, a method of forming aliquid crystal display device having an array substrate includes forminga plurality of gate lines and data lines over the array substrate, thegate and data lines defining a pixel region, forming a thin filmtransistor formed at each crossing region of the gate lines and the datalines, the thin film transistor including a gate electrode, an activelayer, a source electrode, and a drain electrode, forming a black matrixover the thin film transistor, exposing a portion of the drainelectrode, forming a first pixel electrode at the pixel region,contacting the exposed portion of the drain electrode, forming a colorfilter on the first pixel electrode at the pixel region, and forming asecond pixel electrode on the color filter, contacting the first pixelelectrode.

[0030] It is to be understood that both the foregoing generaldescription and the following detailed description are exemplary andexplanatory and are intended to provide further explanation of theinvention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The accompanying drawings, which are included to provide afurther understanding of the invention and are incorporated in andconstitute a part of this application, illustrate embodiments of theinvention and together with the description serve to explain theprinciple of the invention.

[0032] In the drawings:

[0033]FIG. 1 is an expanded perspective view illustrating a related artliquid crystal display device;

[0034]FIG. 2 is a schematic cross-sectional view taken along line II-IIof FIG. 1, illustrating a pixel of the related art liquid crystaldisplay device;

[0035]FIG. 3 is a partial schematic plane view of an array substratehaving a color filter on thin film transistor structure according to thepresent invention;

[0036]FIGS. 4A to 4G are cross-sectional views taken along line IV-IV ofFIG. 3, illustrating the process steps of manufacturing the arraysubstrate according to a first embodiment of the presenting invention;and

[0037]FIGS. 5A to 5F are cross-sectional views illustrating the processsteps of manufacturing the array substrate according to a secondembodiment of the present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

[0038] Reference will now be made in detail to the illustratedembodiments of the present invention, examples of which are illustratedin the accompanying drawings. Wherever possible, the same referencenumbers will be used throughout the drawings to refer to the same orlike parts.

[0039]FIG. 3 is a partial schematic plane view of an array substratehaving a color filter on thin film transistor structure according to thepresent invention.

[0040] As shown in FIG. 3, an array substrate 100 includes a pluralityof gate lines 102 disposed in a transverse direction and a plurality ofdata lines 116 disposed in a longitudinal direction. The plurality ofgate lines 102 and the plurality of data lines 116 cross one anotherdefining a pixel region P. A thin film transistor T is formed at eachcrossing portion of the gate line 102 and the data line 116. The thinfilm transistor T includes a gate electrode 104, an active layer 108, asource electrode 112, and a drain electrode 114. In the pixel regions Pdefined by the plurality of gate lines and data lines 102 and 116, aplurality of color filters 128 are located therein. Additionally, adouble-layered pixel electrode is disposed corresponding to each pixelregion P. A first pixel electrode 126 and a second pixel electrode 130have the same shape. Although not indicated in FIG. 3, the first pixelelectrode 126 is disposed beneath the color filter 128 and contacts thedrain electrode 114, and the second pixel electrode 130 is disposed onthe color filter 128 and contacts the first pixel electrode 126. Namely,the color filter 128 is located between the first and second pixelelectrodes 126 and 130, and the second pixel electrode 130 electricallycontacts the drain electrode 114 through the first pixel electrode 126.

[0041] Meanwhile, a storage capacitor C is included in a portion of thegate line 102 and the storage metal layer 118. Thus, the portion of thegate line 102 acts as a first electrode of the storage capacitor C. And,the storage metal layer 118 acts as a second electrode of the storagecapacitor C. The first and second pixel electrodes 126 and 130electrically contact the storage metal layer 118, so that they areelectrically connected to the storage capacitor C in parallel.

[0042] The array substrate 100 of FIG. 3 has a color filter on thin filmtransistor (COT) structure. In such a COT structure, a black matrix 120and the color filters 128 are formed on the array substrate 100. Theblack matrix 120 is disposed to correspond to the thin film transistorsT and the gate lines 102 and the data lines 116, so that it preventslight leakage in the LCD device. The black matrix 120 is formed of anopaque organic material, thereby blocking the light incident to the thinfilm transistors T. Also, it protects the thin film transistors T fromthe external impact. Moreover, the first pixel electrode 126 disposedunderneath the color filter 128 protects the gate line 102 from adeveloper that damages the color filter 128 in the fabrication process.

[0043]FIGS. 4A to 4G are cross-sectional views taken along line IV-IV ofFIG. 3, illustrating the process steps of manufacturing an arraysubstrate according to a first embodiment of the presenting invention.

[0044] In FIG. 4A, a first metal layer is deposited on the surface of asubstrate 100 and then patterned to form a gate line 102 and a gateelectrode 104. Thereafter, a gate insulation layer 106 (or a firstinsulating layer) is formed on the substrate 100 to cover the gate line102 and the gate electrode 104. The gate insulation layer 106 is formedof an inorganic material, such as silicon nitride (SiN_(x)) and siliconoxide (SiO₂). An intrinsic amorphous silicon layer (a+−Si:H) and then ann⁺-doped amorphous silicon layer (n⁺a−Si:H) are sequentially depositedon the entire surface of the gate insulation layer 106 and thensimultaneously patterned to form an active layer 108. An ohmic contactlayer 110 is then formed on the active layer 108.

[0045] In FIG. 4B, after forming the active layer 108 and the ohmiccontact layer 110, a second metal layer is deposited over the substrate100, and then patterned to form a source electrode 112, a drainelectrode 114, a data line 116, and a storage metal layer 118. Thesecond metal layer may be formed of one of chromium (Cr), molybdenum(Mo), copper (Cu), tantalum (Ta) and an alloy of any combinationthereof. The source electrode 112 extends from the data line 116 andcontacts one portion of the ohmic contact layer 110. The drain electrode114 is spaced apart from the source electrode 112 and then contacts theother portion of the ohmic contact layer 110. The storage metal layer118 overlaps the gate line 102. After that, a portion of the ohmiccontact layer 110 between the source and drain electrodes 112 and 114 isetched by using the source and drain electrodes 112 and 114 as masks.Therefore, a thin film transistor T and a storage capacitor C arecomplete. For example, the source and drain electrodes 112 and 114 maybe formed of a bi-layer of copper/molybdenum. As described withreference to FIG. 3, the thin film transistor T is comprised of the gateelectrode 104, the active layer 108, the ohmic contact layer 110, thesource electrode 112, and the drain electrode 114. And the storagecapacitor C is comprised of the gate line 102, the storage metal layer118, and the interposed first insulator 106.

[0046] Thereafter, a second insulating layer 119 is deposited over theentire surface of the substrate 100 to cover the patterned second metallayer. The second insulating layer 119 may be formed of silicon nitride(SiN_(x)) or silicon oxide (SiO₂) The second insulating layer 119enhances the adhesion of an organic layer to be formed in a later step.The second insulating layer 119 prevents a bad contact between theactive layer 108 and the organic layer. If the bad contact does notoccur between the active layer 108 and the organic material, the secondinsulating layer 119 is not necessary.

[0047] In FIG. 4C, an opaque organic material 120 a having a lowdielectric constant is deposited on the second insulating layer 119. Theopaque organic material 120 a has a black color so that it becomes ablack matrix.

[0048]FIG. 4D shows the steps of forming a black matrix. The opaqueorganic material 120 a formed on the second insulating layer 119 ispatterned, so that a black matrix 120 is formed over the thin filmtransistor T, the data line 116, and the gate line 102. Since the blackmatrix 120 is formed of an organic material, it protects the thin filmtransistor T. A transparent organic or inorganic material may beemployed as a TFT-protection layer instead of the opaque organicmaterial 120 a. However, an additional process of forming a black matrixon the upper substrate is required to use the transparent material. Whenpatterning the opaque organic material 120 a to form the black matrix120, a drain contact hole 122 and a storage contact hole 124 are formedexposing a portion of the drain electrode 114 and a portion of thestorage metal layer 118, respectively. Moreover, when patterning theopaque organic material 120 a, portions of the first and secondinsulators 106 and 119 corresponding to the pixel region P are alsoremoved to expose a portion of the substrate 100. Alternatively, whenpatterning the opaque organic material 120 a, the gate insulation layer106 may remain in order to control the height of a color filter to beformed in a later process. Namely, the height of the color filter isdetermined by the existence of the gate insulation layer 106.

[0049] In FIG. 4E, a first transparent electrode layer 126 of indium tinoxide (ITO) or indium zinc oxide (IZO) is deposited over the entiresurface of the substrate 100 to cover the black matrix 120. The firsttransparent electrode layer 126 contacts the drain electrode 114 throughthe drain contact hole 122 and the storage metal layer 118 through thestorage contact hole 124. The first transparent electrode layer 126prevents a developer for patterning color filters in a later processfrom penetrating into the gate insulation layer 106.

[0050] In step portions of the gate line 102 and gate electrode 104, thegate insulation layer 106 may be formed with poor quality and may havedefects such as pinholes and cracks. Therefore, when patterning thecolor filters, the developer for the color filters may penetrate intothe gate insulation layer 106 and then deteriorate the gate line 102 andthe gate electrode 104. By forming the first transparent electrode layer126, such deterioration can be prevented and process stability can beprovided.

[0051] In FIG. 4F, color resin is formed on the first transparentelectrode layer 126 and then patterned to form the color filters 128 a,128 b, and 128 c. As described above, the color filters 128 a, 128 b,and 128 c for displaying a full spectrum of colors are formed in thepixel regions P. Thereafter, a second transparent electrode layer 130 isformed on the color filters 128 and the exposed portions of the firsttransparent electrode layer 126. The second transparent electrode layer130 is formed of indium tin oxide (ITO) or indium zinc oxide (IZO) likethe first transparent electrode layer 126. As shown in FIG. 4F, thesecond transparent electrode layer 130 contacts the first transparentelectrode layer 126.

[0052]FIG. 4G shows the process step of patterning the first and secondtransparent electrode layers 126 and 130 to form a double-layered pixelelectrode (i.e., often referred as a sandwich pixel electrode). Thefirst and second transparent electrode layers 126 and 130 aresimultaneously patterned with the same mask, so that the sandwich pixelelectrode is formed corresponding to each pixel region P. Alternatively,the first transparent electrode layers 126 may be first patterned andthen the color filters formed thereon. Thereafter, the secondtransparent electrode layer 130 may be patterned. The sandwich pixelelectrode is comprised of a first pixel electrode 126 a and a secondpixel electrode 130 a.

[0053] Accordingly, in the first embodiment of the present invention,the black matrix 120 and the color filters 128 are formed in the lowersubstrate 100, so that the liquid crystal display device can have a highaperture ratio. Further, since the pixel electrode has a double-layeredstructure, the process stability is improved during the fabricatingprocess of the array substrate.

[0054] With reference to FIGS. 5A to 5F, a second embodiment of thepresent invention will now be explained. In the second embodiment, apixel electrode flanks on a drain electrode as well as contacts the endside portion of the drain electrode.

[0055]FIGS. 5A to 5F are cross-sectional view illustrating the processsteps of manufacturing the array substrate of FIG. 3 according to asecond embodiment of the present invention. In the second embodiment ofthe present invention, the formation process of a thin film transistorand a storage capacitor is the same as that of the first embodiment.

[0056] In FIG. 5A, a first metal layer is deposited on the surface of asubstrate 200 and then patterned to form a gate line 202 and a gateelectrode 204. Thereafter, a gate insulation layer 206 (or a firstinsulating layer) is formed on the substrate 200 to cover the gate line202 and the gate electrode 204. The gate insulation layer 206 may beformed of an inorganic material, such as silicon nitride (SiN_(x)) orsilicon oxide (SiO₂). An intrinsic amorphous silicon layer (a−Si:H) andan n⁺-doped amorphous silicon layer (n⁺a−Si:H) are sequentiallydeposited on the entire surface of the gate insulation layer 206, andthen simultaneously patterned to form an active layer 208. Then, anohmic contact layer 210 is formed on the active layer 208.

[0057] In FIG. 5B, after forming the active layer 208 and the ohmiccontact layer 210, a second metal layer is deposited over the entiresubstrate 200 and then patterned to form a source electrode 212, a drainelectrode 214, a data line 216, and an storage metal layer 218. Thesecond metal layer may be formed of one of chromium (Cr), molybdenum(Mo), copper (Cu), tantalum (Ta), and an alloy of any combinationthereof. The source electrode 212 extends from the data line 216 andcontacts one portion of the ohmic contact layer 210. The drain electrode214 is spaced apart from the source electrode 212 and then contacts theother portion of the ohmic contact layer 210. The storage metal layer218 overlaps the gate line 202. Thereafter, a portion of the ohmiccontact layer 210 between the source and drain electrodes 212 and 214 isetched using the source and drain electrodes 212 and 214 as masks.Therefore, a thin film transistor T and a storage capacitor C arecomplete. As mentioned with reference to FIG. 3, the thin filmtransistor T is comprised of the gate electrode 204, the active layer208, the ohmic contact layer 210, the source electrode 212, and thedrain electrode 214. And the storage capacitor C is comprised of thegate line 202, the storage metal layer 218, and the interposed gateinsulation layer 206.

[0058] After completing the thin film transistor T and the storagecapacitor C, a second insulating layer 219 is deposited over the entireof the substrate 200 to cover the patterned second metal layer. Thesecond insulating layer 219 may be formed of silicon nitride (SiN_(x))or silicon oxide (SiO₂). The second insulating layer 219 enhances theadhesion of an organic layer to be formed in a later process. The secondinsulating layer 219 prevents a bad contact between the active layer 208and the later-formed organic material. If the bad contact does not occurbetween the active layer 208 and the organic material, the secondinsulating layer 219 is not necessary.

[0059] In FIG. 5C, an opaque organic material 220 a having a lowdielectric constant is deposited on the second insulating layer 219. Theopaque organic material 220 a has a black color so that it becomes ablack matrix. The opaque organic material 220 a protects the thin filmtransistor T and the storage capacitor C from the external impact. Atransparent organic or inorganic material can be employed as aTFT-protection layer instead of the opaque organic material 120 a.However, an additional process of forming a black matrix on the uppersubstrate is required to use the transparent material.

[0060]FIG. 5D shows the process step of forming a black matrix and afirst transparent electrode. The opaque organic material 220 a formed onthe second insulating layer 219 is patterned so that a black matrix 220is formed over the thin film transistor T, the data line 216, and thegate line 202. In the second embodiment, when patterning the opaqueorganic material 120 a to form the black matrix 220, an end side portionof the drain electrode 214 is exposed unlike the first embodiment.Further, a storage contact hole 224 is formed exposing a portion of thestorage metal layer 218. Moreover, when patterning the opaque organicmaterial 220 a, portions of the first and second insulating layers 206and 219 corresponding to the pixel region P are also removed to exposethe substrate 200. With exposing the end side portion of the drainelectrode 214 in the second embodiment, instead of the drain contacthole 122 in the first embodiment, the contact between the drainelectrode 214 and the first transparent electrode layer 226 can beimproved.

[0061] After forming the black matrix 220, the first transparentelectrode layer 226 formed of indium tin oxide (ITO) or indium zincoxide (IZO) is deposited over the entire surface of the substrate 200,so that it covers the black matrix 220, the thin film transistor T andthe storage capacitor C. The first transparent electrode layer 226contacts the storage metal layer 218 and flanks on the drain electrode314 through the storage contact hole 224. It is difficult to form a tinycontact hole, such as a drain contact hole, through the opaque organicmaterial 220 a, and the residues may be clogged in the contact hole.Therefore, the end side portion of the drain electrode 214 is completelyexposed, as shown in 5D, during patterning the opaque organic material220 a to resolve the contact problem.

[0062] Meanwhile, the first transparent electrode layer 226 prevents adeveloper for patterning color filters in a later step from penetratinginto the gate insulation layer 206. As described above, the stepportions of the gate line 202 and gate electrode 204, the gateinsulation layer 206 may be formed with poor quality and may havedefects such as pinholes and cracks. Therefore, when patterning thecolor filters, the developer for the color filters may penetrate intothe gate insulation layer 206 and then deteriorate the gate line 202 andthe gate electrode 204. By forming the first transparent electrode layer226, such deterioration can be prevented and process stability can beprovided.

[0063] In FIG. 5E, color resin is formed on the first transparentelectrode layer 226 and then patterned to form color filters 228 a, 228b, and 228 c. As described before, the color filters are formed in thepixel regions P. Thereafter, a second transparent electrode layer 230 isformed on the color filters 228 and the exposed portions of the firsttransparent electrode layer 226. The second transparent electrode layer230 may be formed of indium tin oxide (ITO) or indium zinc oxide (IZO)like the first transparent electrode layer 226. As shown in FIG. 5E, thesecond transparent electrode layer 230 contacts the first transparentelectrode layer 226 at both sides of the color filter 228.

[0064]FIG. 5F shows the process step of patterning the first and secondtransparent electrode layers 226 and 230 to form a double-layered pixelelectrode (i.e., often referred as a sandwich pixel electrode). Asshown, the first and second transparent electrode layers 226 and 230 aresimultaneously patterned with the same mask, so that the sandwich pixelelectrode is formed corresponding to each pixel region P. Alternatively,the first transparent electrode layers 226 may be first patterned andthen the color filters formed thereon. Thereafter, the secondtransparent electrode layer 230 may be patterned. The sandwich pixelelectrode is comprised of a first pixel electrode 226 a and a secondpixel electrode 230 a.

[0065] In the second embodiment, the black matrix 220 does not have thedrain contact hole unlike the first embodiment. It is difficult to forma contact hole through the opaque organic material. Therefore, whenforming the black matrix over the thin film transistor, the draincontact hole is not formed to provide the process stability according tothe second embodiment of the present invention.

[0066] According to the present invention, the COT-structural arraysubstrate has color filters with a black matrix. The opaque organicmaterial over the thin film transistor acts as not only the black matrixbut also the TFT-protection layer. Therefore, the present inventionsimplifies the fabrication process and reduces the production cost.Furthermore, since the black matrix is formed in the array substrate, itis not required to consider an aligning margin when designing andaligning the lower and upper substrates, thereby increasing an apertureration.

[0067] It will be apparent to those skilled in the art that variousmodifications and variations can be made in the liquid crystal displaydevice having an array substrate of a thin film transistor structure anda manufacturing method thereof of the present invention withoutdeparting from the spirit or scope of the inventions. Thus, it isintended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A liquid crystal display device having an arraysubstrate, comprising: a plurality of gate lines and data lines over thearray substrate, the gate and data lines defining a pixel region; a thinfilm transistor formed at each crossing region of the gate lines and thedata lines, the thin film transistor including a gate electrode, anactive layer, a source electrode, and a drain electrode; a black matrixover the thin film transistor, exposing a portion of the drainelectrode; a first pixel electrode at the pixel region, contacting theexposed portion of the drain electrode; a color filter on the firstpixel electrode at the pixel region; and a second pixel electrode on thecolor filter, contacting the first pixel electrode.
 2. The deviceaccording to claim 1, further comprising a first insulating layerbetween the gate electrode and the active layer.
 3. The device accordingto claim 2, further comprising a second insulating layer either on thethin film transistor or on the black matrix.
 4. The device according toclaim 2, wherein the first insulating layer is formed of an inorganicmaterial.
 5. The device according to claim 4, wherein the inorganicmaterial is selected from the group consisting of silicon nitride andsilicon oxide.
 6. The device according to claim 2, further comprising astorage capacitor on the first insulating layer.
 7. The device accordingto claim 6, wherein the first pixel electrode contacts the storagecapacitor through a storage contact hole in the black matrix.
 8. Thedevice according to claim 1, wherein the first pixel electrode contactsthe drain electrode through a drain contact hole in the black matrix. 9.The device according to claim 1, wherein the black matrix exposes an endside portion of the drain electrode, so that the first pixel electrodedirectly contacts the end side portion of the drain electrode.
 10. Thedevice according to claim 1, further comprising an ohmic contact layerbetween the active layer and the source and drain electrodes.
 11. Thedevice according to claim 1, wherein the first pixel electrode directlycontacts the substrate.
 12. A method of forming a liquid crystal displaydevice having an array substrate, comprising: forming a plurality ofgate lines and data lines over the array substrate, the gate and datalines defining a pixel region; forming a thin film transistor formed ateach crossing region of the gate lines and the data lines, the thin filmtransistor including a gate electrode, an active layer, a sourceelectrode, and a drain electrode; forming a black matrix over the thinfilm transistor, exposing a portion of the drain electrode; forming afirst pixel electrode at the pixel region, contacting the exposedportion of the drain electrode; forming a color filter on the firstpixel electrode at the pixel region; and forming a second pixelelectrode on the color filter, contacting the first pixel electrode. 13.The method according to claim 12, further comprising forming a firstinsulating layer between the gate electrode and the active layer. 14.The method according to claim 13, further comprising forming a secondinsulating layer either on the thin film transistor or on the blackmatrix.
 15. The method according to claim 13, further comprising forminga second insulating layer on both the thin film transistor and the blackmatrix.
 16. The method according to claim 13, wherein the firstinsulating layer is formed of an inorganic material.
 17. The methodaccording to claim 16, wherein the inorganic material is selected fromthe group consisting of silicon nitride and silicon oxide.
 18. Themethod according to claim 13, further comprising forming a storagecapacitor on the first insulating layer.
 19. The method according toclaim 18, wherein the first pixel electrode contacts the storagecapacitor through a storage contact hole in the black matrix.
 20. Themethod according to claim 12, wherein the first pixel electrode contactsthe drain electrode through a drain contact hole in the black matrix.21. The method according to claim 12, wherein the black matrix exposesan end side portion of the drain electrode, so that the first pixelelectrode directly contacts the end side portion of the drain electrode.22. The method according to claim 12, further comprising forming anohmic contact layer between the active layer and the source and drainelectrodes.
 23. The method according to claim 12, wherein the firstpixel electrode directly contacts the substrate.
 24. The methodaccording to claim 12, wherein the forming first and second pixelelectrodes comprises, depositing a first transparent metal electrodelayer over the substrate; depositing a second transparent metalelectrode layer over the first transparent metal electrode layer; andpatterning the first and second transparent metal electrode layers atthe same time.